1. Field of the Invention
This invention relates to silicon carbide sintered members having improved heat insulating properties, and more particularly to a silicon carbide sintered member having a low thermal conductivity in the vicinity of its surface coated with zirconia.
2. Related Art Statement
The silicon carbide sintered members are superior in the high-temperature mechanical strength, heat resistance, corrosion resistance and so on to the other inorganic materials and metals, so that they are considered to be utilized as a high-temperature structural member, and the development for applications thereof is proceeding widely.
However, the silicon carbide sintered member has drawbacks that the thermal conductivity is high and the heat insulating properties are poor. For instance, when the silicon carbide sintered member is applied to a wall face of an engine combustion chamber for enhancing the heat resistance of this chamber, the heat insulating properties against exterior can be improved by making the air gap or the like, but air supplied into the inside of the room is warmed due to high thermal conductivity to provide no effective inlet gas quantity. In this case, the high thermal conductivity near the surface of the silicon carbide sintered member comes into problem.
In order to improve heat resistance, corrosion resistance and wear resistace, the application of zirconia to a surface of a metal as a substrate through plasma spray coating is disclosed in Japanese Patents laid open Nos. 55-28,351, 57-140,876 and 58-87,273. Furthermore, Japanese Patents laid open Nos. 57-135,771 and 58-125,679 disclose the coating of zirconia onto the surface of carbon substrate. However, there is no example aiming at the improvement of heat insulating properties near the surface of silicon carbide sintered member as a substrate.
The zirconia is low in the thermal conductivity and excellent in the heat insulating properties as compared with the silicon carbide sintered member, but has a drawback that the high-temperature mechanical strength is low.